Automatic party-line selective-signaling system



M. L. NELSON AUTOMATIC PARTY LINE SELECTIVE SIQNAUING SYSTEM Sept. 15, 1925.

4 Shee ts'-Sheet 1 Filed Nov. 10 920 'Sept. 1,5, 1925.

M. L. NELSON AUTOMATIC PARTY LINE SELECTIVE SIGNALI'flG SYSTEM 4 Sheets-Sheet 2 um m\\\ M. L. NELSON Au'rolwnc PARTY LINE SELECTIVE smmuue SYSTEM Filed Nov. 10, 1920 -4 Sheets-Sheet 5 Sept. 15, 1925.

M. L. NELSON AUTOMATIC PARTY LINE SELECTIVE SIGNALING SYSTEM Sept. 15, 1925.

Filed'Nov. 10, 1920 4 Sheets-Sheet '4 --ITTLTETTT H51" I1" w 1 EL' Patented Sept. 15,1925.

UNITED STATES PATENT OFFICE.

MARTIN L. NELSON, or CHICAGO, ILLINOIS, ASSIGNOR TO AUTOMATIC ELECTRIC COMPANY, or CHICAGO, ILLINOIS, a CORPORATION on ILLINOIS.

AUTOMATIC PARTY-QINE SELECTIVE-SIGNALING SYSTEM.

Application filed November 10,1920. Serial No. 423,147.

To all whom it may concern:

Be it known that I, MARTIN L. NELSON, a citizen of the United States of America, and a resident of Chicago, Cook County, and State of Illinois, have invented certain new and useful Improvements in Automatic Party-Line Selective-Signaling Systems, of which the following is a specification.

This invention relates in general to automatio party line selective signaling systems,

but is more particularly concerned with reverting call equipment whereby an auto matic party line subscriber may signal another party on his own line. The object of my invention is to provide ringback switches for handling reverting calls which will operate in conjunction with any standard type of party line.

In the development of the automatic telephone system different types of party lines have been designed and have come into general use. One type, known as harmonic ringing, employs different frequencies of ringing current to ring over a metallic circuit; another, which has just recently come into use in automatic telephone systems, uses positive and negative pulsating current and is known commercially as superimposed ringing. Semi-selective ringing, a system wherein the ringers at each substation on a party line are connected from alternate sides of the line to ground and in which one and two bell code ringing is employed, has also become well known. Still another type, what is known as harmonic two frequency selective, is used to some extent; in this system the ringers at each substation are con-- nected in a manner similar to semi-selective practice, but instead of code ringing two different frequencies of ringing current are used.

Heretofore it has been the practice to provide ringback switches which are designed to operate in the particular type of selective ringing sytem which is in use and which will not operate with any other type. This makes it necessary to manufacture a large number of different types of ringback switches, and this practice, which provides a number of different devices to accomplish the same purpose, is more or less objectionable, as is well understood. The ringback switch herein described, therefore, while it s primarily intended for use in a system usng the superlmposed type of selective ringing, has been specially designed so that it Wlll also operate without change in any of the other selective ringing systems mentloned thus rendering it unnecessary to manufacture more than the one type of switch, and enabling operating companies to take care of all reverting calls in their systems regardless of how many different types of selective ringing are in use.

Referring now to the drawings, in Fig. 1 three types of party lines are shown, using three different types of selective signaling, namely, harmonic, shown at A, superimposed, shown at A, and semi-selective,

. shown at A Only one substation on each party line is shown in full, the other substations being represented by their ringers which are connected in the proper manner. It will be understood that the omitted circuits are in each case identical with the one shown. Each party line has a rotary line switch individual to it, only the line switch C individual to the party line A being shown. All the rotary line switches have access to first selectors, and one of the selectors, accessible to the line switch C is the selector shown at D. These first selectors are of the usual Keith-Erickson two wire type and have access at the first level of bank contacts to a plurality of ringback switches one of which is shown at E, Fig. 2. This switch is of a simple one motion type adapted to rotate its shaft carrying the wipers 88 and- 89 in response to impulses from a calling subscriber.

Figs. 3, 4 and 5 show the three classes of rlnging equipment to be used in conjunction with each type of party line illustrated in Fig. 1, the harmonic ringing equipment being shown in Fig. 4, the superimposed in Fig. 3, and the semi-selective in Fig. 5.

Having briefly set forth and described the apparatus shown in the drawings, its operation .will now be considered more in detail.

To enable each party on a party line to call every other party on his own line each subscriber is provided with a card, on which are listed the numbers he will have to dial to call the other parties on his own line. Of the severalparty lines illustrated in Fig. l I will first consider the operation of the reverting call system in'connection with the so called superimposed type of party line, reference being had to Figs. 1, 2, and 3. Below is given the complete list of'numbers which enable the subscribers on this type of party line to call the other parties on the line. i

. Calling stfimo station Dial No.

Certain numbers are also provided for inspectors to test the bells at the various substations on the type of party line and these are:

For station No. 1 ringback dial 19 For station No. 2 ringback dial 10 For station No. 3 ringback dial 17 For station No. 4 ringback dial 18 For the purposes of the description let us assume that the subscriber at substation number 1 on the party line A desires to call the subscriber at station number 2. To do this it will be seen from the number table of call numbers that the calling subscriber will operate his dial for the number 16. Upon removing his receiver, preparatory to making the call, a circuit is completed for the line relay 5, from ground G over the line conductors 3 and 2 in series, thence through the winding of relay 5 to battery. Assuming that the trunk line upon which the wipers 6, 7, and 8 are resting is idle, when the relay 5 energizes and completes the circuit of the switching relay 4, the latter relay will operate at once with the result that the line conductors 2 and 3 are disconnected from the winding of line relay 5 and ground, respectively, and are extended by way of armatures 12 and 14 and their working contacts, wipers 6 and 8, and bank contacts 9 and 11 to the upper and lower windings of line relay 25 of the selector D. p

Upon the line being extended to the selector D, as above described, relay 25 will energize and close the circuit of the slow acting release relay 26. Upon energizing, this latter relay prepares the vertical magnet circuit at armature 27 and its front contact, and at armature 28 aiid its front contact places ground on release trunk conductor 29, thereby establishing a holding circuit which extends by way of bank contact 10, wiper 7, armature 13 and its front contact, winding of switching relay 4, and the winding of the stepping magnet to battery. This holding circuit is completed before the slow acting line relay 5 has deenergized. Besides maintaining the switching relay energized, this holding circuit serves to place ground onmultiples of the test contact 10 and also on multiple test contacts in which the private normal conductor 31 terminates in the banks of the connector switches which have access to the party line A, thus guarding the connection from intrusion in the well known manner.

The calling subscriber may now operate his calling device for the first digit of the desired number which in this case is the digit 1. One interruption is thereby pro duced in the circuit of line relay 25, which on retracting its armature, completes a circuit for the vertical magnet 32 in series with the slow acting relay 33. By the operation of vertical magnet 32 the switch shaft is raised one step thereby placing the wipers 34, 35, and 36 opposite the first level of bank cont-acts, where the trunk lines leading to ringback switches or frequency selectors such as the ringback switch E are terminated. Slow acting relay 33 energizes in series with the vertical magnet and upon the first vertical step of the shaft the off normal springs 37 and 38 close and a circuit is thereby completed from ground on conductor 29, through armature 39 and its working contact, springs 38 and 37 and the winding of relay 40 to battery. Relay 40, on attractin its armature 41, completes a locking circuit for itself and at armature 42 prepares'the circuit of rotary magnet 43, all in a well known manner. An instant after the operation of vertical magnet 32 slow acting relay 33 deenergizes, thus completing the circuit of rotary magnet 43, which operates to rotate the wipers 34 to 36, inclusive, into engagement with the first set of bank contacts in selected level. In operating the rotary magnet breaks the locking circuit of relay 40, which accordingly deenergizes and breaks the circuit of the rotary magnet, which then deenergizes also. The further operation of the selector D depends upon whether or not the trunk line, with which the selector wipers are now associated is busy or idle. If busy, ground will be present on the test contact engaged by wiper 35, and a circuit is thereupon completed from the said grounded bank contact engaged by the test wiper 35, by way of this wiper and conductor 59 and through the winding of relay 40 to battery. Relay 40 operates as before to close the rotary magnet circuit. The rotary magnet 43 then operates to advance the wipers onto the terminals of the next trunk line and also to open the circuit of the relay 40. This alternate operation of the relay 40 and the rotary magnet 43 Wlll continue until an idle trunk line is found, which it will be assumed is the trunk line comprising conductors 55, 56, and 57. The rotation of the switch will now cease and switching relay 44, which has hitherto been shorted out, will energize in series with relay 40, extending the calling subscribers line at armatures 52 and 54 and their front contacts, over trunk conductors 55 and 57, armatures 101 and 102 and their working contacts, to theupper and lower windings of line relay 100 of the ringback switch Relay 100, on energizing, completes a circuit from ground G, by way of armature 103 and its front contact, conductor 104, resting contact and armature 105', and thence through the winding of the slow acting release relay 107 to battery. Relay 107 energizes and at armature 108 and its front contact prepares the circuit of rotary magnet 114, and at armature 109 and its frontcontact places ground G on conductor 56. This ground extends back to the switching relays 44 and 4 of selector D and lineswitch C, respectively, and maintains thes switches in their 0 erated position.

Upon the subscriber at station 1 operating his calling device for the next and final digit of the required number, namely, the digit 6, six interruptions are produced in the circuit of line relay 100, which deenergizes a plurality of times in response to these interruptions. At each retraction of its armature 103 a circuit is completed extending from ground G, by way of armature 103 and its back contact, armature 108 and its front contact, conductor 110, normally closed contact springs controlled by armature 118, slow acting relay 112, conductor 113, and rotary magnet 114 to battery. Magnet 114 operates to rotate the shaft thus carrying the wipers 88 and 89 into engagement with the sixth set of bank contacts. Upon the first rotary step of the switch shaft, springs 115 close, thereby completing a circuit from ground G, through springs 115, conductor 116, and through the winding of relay 117 to battery. Relay 117 energizes, prepares the release magnet circuit, and opens the rotary magnets original energizing circuit. Because of the fact that slow acting relay 112 has attracted its armature and closed an auxiliary path for the rotary magnet the operation of relay 117 will have no eifect at this time.

No further operation of the switch E will take place until the subscriber at station 1 re )laces his receiver on the switchhook. W hen this occurs the line relay 100 will deenergize and complete a circuit extending from ground G, through armature 1'03 and its back contact, armature 108 and its front contact, conductor 110, front contact and armature 118, conductor 119, armature 120 and its back contact, armature 121 and its resting contact, conductor 122 and through the winding of relay 123 to battery.

Relay 123 attracts its armatures and completes' a circuit extending from ground G, by way of armature 124 and its front con tact, conductor 104, back contact and armature 105, conductor 106 and slow acting relay 107 to battery. This circuit maintains relay 107 energized, thereby preventing the release of the switches E, D, and C. ()n at.- tracting its armature 130, relay 123 places ground on conductor 145 extending to the by opening the circuit of relay 136, which i does not energize at 'this time. Relay 135, however, energizes and breaks the circuit of rotary magnet 137, which on its back stroke advances the wiper 138 one step and at the same time again completes the circuit of relay 136. On energizing, relay 136 opens the circuit of relay 135, which relay on deenergizing again completes the rotary magnet circuit. The alternate operation of these relays andthe motor magnet will take place as long as ground is present on conductor 145, that is, as long as any ringback switch is in its operated position.

Still another result of the energization of relay 123 is that the ground placed on conductor 145 also extends through terminals 126 and 127, armature 140 and its front contact, conductor 141, springs 142, and through the winding of relay 143 to battery. Relay 143 energizes, locks itself to ground on conductor 56 at armature 144, and prepares the ringing circuit at armatures- 131 and 132 and their front contacts. The terminals 126 and 127, and 128 and 129 are terminals located on any convenient part of the switch E and in the system now under consideration terminals 126 and 127 are connected together.

Upon wiper 138 reaching the first contact of the interrupter switch bank, ground is placed by-the said wiper on conductor 170, whence a circuit extends through the winding of relay 171 to battery. On energizing,

relay 171 places negative pulsating current from the ringing generator V, extending over conductor 151 to the sixth contactin th upper bank of ringback switch E, thence over wiper 88, front contact and armature 131, ring out off relay 175, front contact and armature 101, trunk conductor 55, hank contact 49, wiper 34, front contact and armature 52, and thence over the upper line conductor 2 through the condensers of substation 1 and 2 and the relays 176 and 177 in multiple to ground. Relays 176 and 177 energize, bridging the ringers of substations'numbers 1 and 2 across the line. The ringenpf substation number 1 is adjusted torespond to negative pulsating current while that of substation number 2 responds to positive pulsating current, therefore the ringer of substation number 1 only will be actuated as long as relifi 171 remains energized. However, as soon as wiper 138 of the interrupter I engages the third bank contact, relay 171 deenergizes, opening the/above traced ringing circuit, and a circuit is then completed in an obvious manner for relay 172 by the wiper 138, which relay, on energizing, places positive pulsating current, at armature 178, on conductor 151 extending back to the ringers of substations numbers 1 and 2 but instead of ringernumber 1 responding the ringer of substation number 2 is actuated by this positive pulsating current. Upon wiper 138 of interrupter reaching the sixth contact a circuit is a ain completed for relay 171 and as the ank contacts of this interrupter are multipled alternately to conductors 170 and 179 the relays 171 and 172 will be successively operated to alternately ring substations numbers'l and 2. hen the subscriber at station 2 removes his receiver from the switchhook a path for direct current is provided through the ring cut off relay 175 extending from battery at any one of the batteries B, B B depending upon whether the receiver is removed during one or the other of the ringing operations or a silent period, over the previously traced ringing circuit through the switchhook springs, transmit ter and receiver of substation number 2, thence over the lower heavy line conductor through switches C, D, and E, wiper 89, and conductor 161 to ground. Relay 175, while it is adjusted not to respond to alternating current, will operate over this circuit and at armature 180 complete the circuit of relay 181. On its energization, relay 181 opens the circuit of slow acting relay 107 at armature 105, and locks itself to off normal ground G at armature 182. Relay 107 deenergizes thereby removing ground from the release trunk conductor 56 at armature- 109, and completing the release magnet circuit at armature 108 for the release of ringback switch E. Ground being no longer present on conductor 56, there will be no holding circuit for the switching relays 44 and 4 of the selector D and lineswitch C, and accordingly these relays will deenergize, relay 44 completing the circuit of release magnet 60.0f selector D. The relay 4 on deenergizing completes the circuit of the line relay 5, the subscriber at station 2 having closed the usual bridge across the line co-nductors'2 and 3 upon removing his receiver from the switch hook. Lineswitch C will operate in the usual manner to extend the line conductors to the upper and lower windings of line relay 25 of selector D in a manner hereinbefore described.

Upon the ringback switch E restoring to normal all the relays assume their original position and as ground is removed from the conductor 145, the interrupter and its associated relays will stop operating.

The subscriber at station 1, who is the calling subscriber, no longer hearing his bell being actuated, knows that the subscriber at station 2 has responded and will remove his receiver. Conversation may no take place in an ordinary manner, battery being supplied to both subscribers from the upper and lower windings of line relay 25 of the selector D. When the conversation is terminated the release of the apparatus will take place in an ordinary manner up' on both subscribers replacing their receivers upon the switchhooks.

The operation of the system when the subscriber at station 1 desires to call the subscriber at station 3 will now be described, the number to be called inthis case being the number 12. The operation of lineswitch 0, selectorD, ringback E, and interrupter I is identical with that hereinbefore described, except that the wipers 88 and 89 of the switch E will be rotated into engagement with the second set of bank con-' l'acts." Now when the relay 171 pulls up a circuit for negative pulsating ringing current will be eflective extending from the generator V throughbattery B, by way of front contact and armature 185, conductor 157, wiper 89, lower line conductor 3, and thence through the condensers and windings of relays 186 and 187 of substations number 3 and number 4 in multiple, to ground. Relays 186 and 187 will operate to bridge the ringers of substations numbers 3 and 4 across the line and because negative pulsating current is flowing only the ringer of substation number 3 responds. Now when relay 171 deenergizes this ringing circuit is opened and when relay 17 2 energizes a new ringing circuit is completed for negative ringing current at armature 188 and its front contact extending over conductor 147, wiper 88 and thence over a previously traced ringing circuit to the ringer of substation number 1 which is actuated as before described. "1 is alternate ringing of the subscriber at station 3 and the subscriber at station 1 will continue until the subscriber at station 3 answers, after which the same operations as hereinbefore described will take place.

Let us now consider the case'.when the subscriber at station 1 calls the subscriber at station 4; to do this he will dial the number 14 as will be seen from the table given hereinbefore. As the operations 'of the lineswitch C, selector D, and ringback E, have been fully described before it will only be necessary to consider the ringing operation when the wipers 88 and 89 of ringback switch E are resting on the fourth set of bank contacts. When relay 171 energizes a circuit is completed at armature 185 for negative ringing current over conductor 149, wiper 88 and thence to substations numbers 1 and 2 in multiple over the upper heavy line conductor. Only the ringer at substation number 1 will be actuated, however, and the subscriber thereat will know that his call is proceeding satisfactorily. When relay 172 pulls up positive pulsating current flows from the generator V, through front contact and armature 189, conductor 159, thence over wiper 89, and the lower heavy line conductor to the ringers of substations 3 and 4, but as only the ringer of substation 4 responds to positive pulsating current the subscriber at station 4 will be signalled. This ringing continues until the called subscriber answers, whereupon the same operations will take place as hereinbefore described.

It will be seen therefore that any subscriber on the partly line A may call any other party on his own line and the ringing at the calling and called substations will be rung alternately until an answer is obtained. The case where any of the parties not mentioned above, call any other subscriber on the party line, is very similar to those already described and it will be unnecessary to explain these operations.

It is sometimes desirable also, to be able to ring only one-substation bell instead of two, this being the case when a repairman desires to test the ringer of any substation on the party line.

For this purpose four extra sets of bank contacts are provided in the ring back switch E, namely, the seventh to the tenth, inclusive, and if one of these contact sets is called but one kind of ringing current is sent out on only one side of the party line A, thereby signaling only the one station which is responsive to that particular type of ringing operation,

As before stated, the ringback switch E is adapted to operate in a system that employs harmonic y g eg, and s peratles i these conditions ringback switches similar.

to the ringback switch E will be provided which have access to ringing equipment such as that shown in F ig, 4. Below is a table which gives the complete list of numbers which the subscribers on the party line A Frill dial to call the other parties on the said Calling stfition station Inspectors testing numbers.

Station No. Dial In order to describe the operation of this system it will be assumed that the subscriber at station 1 on the party line A desires to call the subscriber at substation 2, in which case it will be seen that the said subscriber will operate his calling device for the number 11, and it will be assumed further that the same switches are used as were described in connection with the other party line. Upon removing his receiver from the switchhook the lineswitch individual to his line operates to select an idle trunk line assumed to be the trunk line terminating in selector D. When the first digit of the number is called one interruption is produced in the circuit of the relay 25, which operates to send one impulse of current to the vertical magnet 32, in series with theslow acting relay 33. Magnet 32 operates as before to step the wipers 34 to 36, inclusive, opposite the first level of bank contacts in which terminate trunk lines leading to ringback switches. Upon the first vertical step of the switch, off normal springs 37 and 38 close and a circuit is then completed for the interrupter relay 40, which looks itself to ground at armature 41 and prepares the rotary magnet circuit at armature 42. This latter circuit is completed upon the deenerg ea en 91? sl w acting relay 33 a d t e elector D now operates under control of interrupter relay 40 and test wiper 35 to select an idle trunk line which, it will be assumed, terminates in the ringback switch E.

' Upon the last digit of the number being called, in this case the digit 1, one interruption is produced in the clrcuit of l1ne relay 100, which operates as before to send one impulse to the rotary magnet 114 1n series with the slow acting relay 112. Magnet 114 operates to advance the Wipers 88 and 89 on to the first set of bank contacts. Upon the first rotary step of the switch the rotary off normal springs 115 close thereby completing a circuit for relay 117. When the subscriber at station 1 replaces his receiver on the switchhook an impulse of current is sent to relay 123, which energizes and locks, and at the same time places ground on conductor 145 thereby energizing relay 143, which also looks. The ground on conductor 145 also extends to the ringing interrupter I. This interrupter is identical with the interrupter shown at I, Fig. 3, and will operate in a similar manner, actuating alternately the relays 200 and 201, and 202. Relay 200, on attracting its armature 203, places 16 cycle ringing generator on conductor 146 extending by way of conductor 146, wiper 88, over the upper heavy line conductor, condensers and ringers of the substations on party line A in multiple, and thence over the lower heavy line conductor, wiper 89, to ground on conductor 156*. As only the ringer of substation number 1 is tuned to 16 cycle ringing current only the subscriber at station 1 will be signalled. When relay 202 energizes, attracting armature 205, 33 cycle ringing current will be placed on the conductor 146 extending back to the party line substations but in this case the ringer of substation number 2 being 33 cycle, will be actuated. Thus substations numbers 1 and 2 will continue to be rung alternately, until an answer. is obtained. When this occurs a circuit for ring cut off relay 175 is completed from battery 13 through a ringing generator, over the upper line conductor, switchhook, transmitter and receiver of the called substation, lower line conductor, and wiper 89 to ground G. This circuit for relay 175 is efi'ective if the receiver of the called station. is removed during a ringing period; if however, the receiver is removed during a silent period battery is supplied to the above traced circuit from 13. Upon the ring out off relay 175 energizing the same operations as hereinbefore described take place. It will be seen from the table of numbers given that the first six bank contacts of ringback switch E are necessary to signal the various combinations of calling and called subscribers on the party line A. These calls are similar to the one above described and hence, will be unnecessary to explain.

'The seventh to the tenth sets of bank contacts, inclusive, are provided as in the case of the superimposed ringing equi ment, for inspectors ringbacks to test the 11s at the various substations on the party line. In this .case but one frequency of mu ing current is sent back over party line as it is only necessary to ring the particular bell Wl'llCll is to be tested.

The operation of the ringback switch E when used in a semiselective ringback system, will now be described. For this purpose let us suppose that the party line A has a rotary lineswitch individual to it which has access to selector switches similar to the selector D and that ringback switches similar to the ringback switch E are provided which have access to the ringing equipment shown in Fig. 5, instead of that shown in Fig. 4. The following is a complete list of the numbers which the subscribers on the party line A will dial to call the other parties on his line.

- Calling Station static D181 No. No

subscriber at station 1 will operate his calling device for the number 10. Upon removing his receiver, the lineswitch individual to this party line operates as before to select an idle selector assumed to be the selector D. When the digit 1 is called the selector D operates in the usual manner, stepping its wipers up opposite the first level of bank contacts and then rotating to find an idle trunk line which, it will be assumed, terminates in the ringback switch E. When the last digit is called, in this case the digit 0, ten interruptions are produced in the circuit of line relay 100 of the switch E and the line relay operates to control the rotation of wipers 88 and 89 on to the tenth set of bank contacts. When the calling subscriber hangs up his receiver relay 123 energizes as before, placing ground on conductor 145, but this does not extend to relay 143 as in the two prior systems because the tie between terminals 126 and 127 is omitted in this case. This ground extends from G, armature,130 ,"con-. v

ductor 145, conductor 145, and through the winding of relay 266 to battery. -Re1ay 266 energizes, at armature 267 connects battery to the conductor 268 extending to the various ringing relays, and at armature 269 places ground on conductor 270 extending through the solenoid winding of the ringing interrupter H to'battery. This interru ter is of the usual construction adapted w en the winding 271 is energized to pull up the shaft carrying the wiper 272 quite rapidly. Upon wiper 272 reaching the top contact 273, pin 274 is so adjusted that it moves the lever 275 into its alternate position where it looks, opening the circuit of solenoid winding 271 at springs 276 and 277 and placing ground on right hand contacts engaged by wiper 27 2, at springs 276 and 278. The circuit of solenoid 271 now being broken, the shaft 279 slowly returns to normal, placing ground successively on the contacts 273, 280 and similar contacts by means of the wiper 272. Upon the shaft reaching normal, pin 281 engages the lever 275 and moves it into its original position, removing ground from the right hand contacts engaged by wiper 272 and again completing the circuit of solenoid 271. These operations continue as long as ground is present on conductor 270, that is, as long as any ringback switch having access to the interrupter H and its associated ringing equipment is in an operated position.

The wipers 88 and 89 of switch E being now in engagement with the last set of bank contacts, when wiper 272 engages contact 273, on its downward stroke, ground is placed for a short time on conductor 282, extending through the winding of relay 283 to battery on conductor 268. Relay 283 energizes and at armature 290 and its front contact places ground on conductor 291 extending by way of armature 140 and its make contact, conductor 141, springs 142 and through the winding of relay 143 to battery. Relay 143 energizes, locks itself to ground G at armature 144 and its front contact, and prepares the ringing circuit at armatures 131 and 132. The tie between the terminals 126 and 127 on the ringback E was omitted in this case for the reason that as soon as one ringback switch, having access to the ringing equipment shown in Fig. 5 operates, the interrupter begins to operate thus actuating the various relays to supply ringing current to the bank contacts of the several ringback switches. Now it might happen that another ringback switch E would be operated and if relay 143 pulled up immediately upon relay 123 operating, as in the cases described before, and at this time the interrupter H was in an intermediate position on its down stroke, a series of code rings would be sent to the line of the subscriber who had operated ringback switch E. As the various stations on the party linerespond to different code rings it will readily be seen that a certain amount of confusion would be likely to arise due to the Wrong subscriber being signalled. To

obviate the above difliculty relay 143 is notenergrzed untll the wiper 272 of interrupter H is 1n engagement with the first contact 273 on its downward stroke. Relay 283, on

energizing, also places ground on conductor 293 at armature 294 whence it extends through the winding of relay 288 to battery. When wiper 272 reaches the next contact 280, ground is placed on conductor 299 extending to relay 284. This relay also places ground on conductor 293thereby maintaining relay 288 energized. At this time however, the energization of these relays has no effect. Upon contactor 272 engaging contact 292 ground is placed on conductor 295 extending through the winding of relay 285 to battery. Relay 285 energizes and at armature 296 and its front contact places generator G on conductor 297 extending by way of conductor 155", conductor 155, wiper 88, upper heavy line conductor, and thence through the condensers and ringers of substations numbers 1 and 2 on the party line A to ground. This will actuate both bells for a short period. When wiper 27 2 engages contact 298 a circuit is completed for relay 286 but its operation will be uneffective at present. On reaching contact 299' wiper 27 2 places ground on conductor 300 extending through relay 287- to battery. On energizing, relay 287 places generator at armature 301 on conductor 297 for another short interval. The ringers at substations numbers 1 and 2 are thus actuated for two short rings and station number 2 being a two bell station, the subscriber thereat will know he is being called. The ringing of the subscriber at station 1 will notify him that his call is proceeding satisfactorily. This ringing will continue until the subscriber at station 2 removes his receiver from the switchhook whereupon a circuit for the ring out off relay 175 is. completed from battery B during a ringing period, or 13", during asilent period, thence over the wiper 88, upper line conductor, through receiver and transmitter of the called substation, lower line conductor, and wiper 89 to ground G Upon energizing, relay 175 initiates the release of the switches and the remaining operations of this system are identical with those described hereinbefore.

The operation of this system when the subscriber at station 1 on the party line A wishes to call the subscriber at station 3 on the same party line will now be described. It will be seen from the table that the number to be dialed is-11. Upon the receiver being removed, the line switch individual to the party line A will operate as before to select an idle trunk which it will be assumed terminates in selector -D.

Upon the subscriber at station 1 operating his calling device for the first digit 1, one interruption is produced in the circuit of line relay 25. Theline relay 25 operates as before, controlling the operation of the selector D in stepping to the first leveland selecting a trunk line leading to an idle ringback switch which we will assume to be E. When the last digit is called the line relay 100 of the switch E responds thereto and causes the wipers 88 and 89 to rotate into engagement with the first set of bank contacts in the usual manner. Upon the calling subscriber hanging up his receiver the interrupter H operates starting the signaling of the two substations, the circuits of which will now be traced.

When the wiper 27 2 of the interrupter H engages contact 273 on its downward stroke, a circuit is completed for the relay 283. This relay on attracting its armature 290, places ground on conductor 291 extending to relay 143 of the ringback switch, this latter relay operating to prepare the ringing circuit. Relay 283 at armature 299 also completes the circuit of the relay 288. Upon wiper 272 engaging the contact 280, relay 284 is energized. Relay 284 on attracting its armature 302 maintains relay 288 energized after the relay 283 has deenergized. When relay 288 attracts its armatures, a

' circuit is completed from generator G on conductor 304 by way of the front contact and armature 303, over conductor 305, conductor 146 conductor 146, upper line conductor, and thence through the condensers and ringers of substations numbers 1 and 2 in multiple to ground. As relay 288 maintains its armature attracted while the wiper 272 of interrupter H is passing over two bank contacts, one long ring is sent over this ringing circuit, thereby signaling substation number 1. As wiper 272 of the solenoid H engages contacts 292 and 298 a circuit is successively completed for relays 285 and 286 and as each closes the circuit of relay 289 one long ring is sent from the generator G on conductor 304 by way of front contact and armature 305, conductor 156 conductor 156, bank contact and wiper 89, lower heavy line conductor, and through the condensers and ringers of substations numbers 3 and 4 in multiple to ground. This ring will serve to signal substation number 3 which is also a one bell station. The ringing of the subscribers at these stations will continue alternately as described, until the party at station 3 answers. When this occurs the ringing stops and the switches release as before described, after which the conversation will be-carried on in the ordinary manner.

operates to select an idletrunk terminating in a selector, which we will assume is the selector D. In response to the first digit of the number the selector will step opposite the first level and rotate to find an idle trunk line leading to a ringback switch. This ringback will be assumed to be the switch E. The subscriber at station 1 now sends three impulses to this ringback switch whereupon it rotates its wipers 88 and 89 to the third set of bank contacts. When the calling subscriber replaces his receiver on the. switchhook the ringing operation is initiated in the ordinary manner. As before, when wiper 272 engages contacts 273 and 280, a circuit is successively completed for the relays 283 and 284. On energizing, each of these relays close the circuit of relay 288 which operates to send one long ring to substations numbers 1 and 2 over the previously traced ringing circuit. Upon wiper 27 2 engaging contact 292, the relay 285 energizes and at armature 307 sends 1 short ring to substations 3 and 4. Relay 287 is energized as wiper 272 contacts with the contact 299 and at armature 306 sends another short ring to stations numbers 3 and 4. The remaining operations of this last case are identical with any of the former ones and will therefore be readily understood.

Certain of the calls given in the number table have not been described, but ony one of these is similar to one of the three typical cases above explained and it will therefore,

be unnecessary to go into their operation.

The operation of the ringback switch E will now be briefly explained in the system known as harmonic two frequency selective. For this purpose the party line will be represented by A but the ringers of the substations thereon will be of the harmonic type, connected in the same manner as the semiselective ringers. The bells of substations 1 and 3 are adapted to respond to 33 cycle ringing generator while those of substations 2 and 4 respond to 50 cycle ringing current. Ringback switches similar to the switch E will be used having the tie between the terminals 126 and 127 and will have access to the ringing equipment shown in Fig. 3. However in place of the positive and negative pulsating current ringing equipment, two generators of diiferent frequencies will be employed, a 33 cycle generator taking the place ofthe negative battery B', and a 50 cycle generator being substituted for the positive battery B .v Of course generator V will not be used in this case. The ringing operation would be similar to the superimposed ringing first described and will be readily understood by reference to that description.

Referring now to the ringback switch '1), as mentioned before, th terminals 128 and 120 are mounted upon any convenient part of the switch and are tied together when the first selectors are equipped with dial tone..

' cally impossible in the case of a reverting call. To obviate this the terminals 128 and 129 of the ingback switch 1*] are connected together, Under thes conditions when the called subscriber answers, ring out off relay 175 will energize as before and complete the circuit of relay 181. On operating, relay 181 will not be elfective to open the circuit of slow acting release relay 107 as the break contact at armature 105 will be short circuited by the tie between the terminals 128 and 129. However, relay 181 will open the locking circuit of relay 123 at armature 121. Relay 123 on deenergizing will open the ringing circuit and connect the upper and lower line conductors to the windings of line relay 100 of ringback switch E. Battery will then be supplied for conversational purposes from this relay and the release will take place in a well known manner upon both subscribers replacing their receivers on th switchhook.

In view of all the foregoing, it will be seen that I have devised a highly improved ringback switch which is adapted to operate without change with any standard type of party line.

Having fully described and disclosed the features of my invention, what I consider to be new and desire to have protected by Letters Patent will be pointed out in the appended claims.

What I claim as my invention is:

1. In an automatic telephone system, a party line having substation-ringers connected in bridge of the line and each adapted to respond to a different frequency of ringing current, a second party line having substation ringers connected from opposite sides of the line to ground, the two ringers on each side of th line being responsive to positive and negative pulsating currents, respectively, a third party line comprising one and two bell stations in which the ringers are connected from opposite sides of the line to ground, dilferent kinds of signaling apparatus for selectively signaling the stations on said party lines, and a plurality of interchangeable ringback switches associated with said signaling apparatus for handling thercverting calls.

2. In a telephone system, a part line, a ringing generator, two leads extending from said generator, batteries of opposite po larity connected in series with said leads, respectively, a riugback switch, means controlled over said line for operating said ringback switch, a pair of ringing relays, contacts on said relays-selectable by said ring-back switch, and a rotary switch controlling said relays for variably connecting said leads to the conductors of said line to selectively signal the stations thereon.

6. In a telephone system, a party line,

four ringing generators, each supplying a different frequency of ringing current, a ringback switch, means controlled over said line for operating said rlngbackswitch to select two of said generators, a rotary switch controlled by said ring back switch, ringing relays inserted between the said ring back switch and said generators, and circuits over which said rotary switch controls said relays for alternately connecting said selected generators to said line to selectively signal two stations thereon. v

4. In a telephone system, a party line, a ringing generator, a rotary switch, relay IIIBChtLIllSll'l, a ringback switch controlled from said line for causing a variable operation of said rotary switch and relay mechanism to apply ringing current from said generator to said line' to selectively signal a station thereon, release means in said ringback switch, means controlled by the removal of the receiver at said called station for operating said release means, terminals in said ringback switch adapted to be connected by hand to render said removal ineffective to operate said release means during a subsequent call, and means then operative responsive to the replacement of the receiver at said called station for operating said release means.

5. In a telephone system, a party line, a ringing generator, a rotary switch, relay mechanism, a ringback switch, a selector switch controlled from said line for extending a connection to said ringback switch, means for then operating said ring back switch, means controlled by said ringback switch for causing a variable operation of said rotary switch and relay mecha nism to apply ringing current from said generator to said line to selectively signal a station thereon, a battery feed relay in said ringback switch, a battery feed relay in said selector switch, means responsive to the re moval of the receiver at said called station for supplying talking current thereto from said battery feed relay in said ringback switch, and means in said ringback switch for changing the connections thereof so that on a subsequent call talking current will be supplied to the called station responsive to the removal of the receiver from the windings of said battery feed relay in said selector.

6. In an automatic telephone system, a party line having substation ringers connected in bridge of the line and each adapted to respond to a diflerent frequency of ringing current, a party line having substation ringers connected from opposite sides of the line to ground, the two ringers on each side of the line being responsive to positive and negative pulsating currents, respectively, different kinds of signaling appa ratus for selectively signaling the stations on said party lines, and a plurality of interchangeable ringback switches associated with said signaling apparatus for handling the reverting calls,

7. In an automatic telephone system, a party line having substation ringers connected in bridge of the line and each adapted to respond to a different frequency of ringing current, a second party line comprising one and two bell stations in which the ringers are connected from opposite sides of the line to ground, different kinds of signaling apparatus for selectively signaling the stations on said party lines, and a plurality of interchangeable ringback switches associated with said signaling apparatus for handling the revertive calls.

8'. In an automatic telephone system, av

party line having substation ringers connected from opposite sides of the line to ground, the two ringers on each side of the line being responsive to positive and negative pulsating currents, respectively, a second party line comprising one and two bell stations in which the ringers are connected from opposite sides of the line to ground, different kinds of signaling apparatus for selectively signaling the stations on said party lines, and a plurality of inter-' back switches being interchangeable between groups, a selector switch having access to the various groups of ringback switches, means controlled from a station on a party line of any one of said types for operating said selector to select a ringback switch in a particular group, and means for then operating said selected ringback switch Whereby said associated signaling apparatus is caused to function to selectively signal a station on the calling party line.

Signed by me at Chicago, Cook County,

Illinois, this 28th-da of Oct., 1920.

- MA TIN L. NELSON. 

